Ultraviolet (UV) light radiation is known to be a factor that damages wood, paints and other protective or decorative coatings, plastics, various textiles made from natural and manmade fibers and keratin substrates including human skin and hair. Damage to human skin, for example, can include loss of skin elasticity and the appearance of wrinkles, erythema and skin burning and the inducement of phototoxic or photoallergic reactions. Hair damage by UV light is perceived as dryness, reduced strength, rough surface texture, loss of color and luster, stiffness and brittleness.
In the case of plastics, UV exposure can result in loss of tensile strength, embrittlement and discoloration. UV exposure can also result in fading of painted surfaces or dyed textiles. To help prevent such degradation, ultraviolet light stabilizers are often incorporated into a polymer composition, which is used as a protective top layer for underlying materials.
Protection of exposed skin and hair from UV exposure can be effected by applying directly to the skin and hair a preparation containing a UV-absorbing moiety.
Generally, sunscreens for application to the hair require substantivity (adhesion) to the hair, and compatibility in hair care formulations which are often water-based.
Many sunscreen agents, however, do not fully meet these requirements. Thus the level of sunscreen agents that could be incorporated into hair care formulations and/or the level of sunscreen agents that can deposit on the hair are limited. Accordingly, there is an ongoing need for new sunscreen agents with improved substantivity and water solubility for incorporation into aqueous formulations.
Skin and hair can also be protected by covering with clothing, thereby avoiding direct exposure of the skin and hair to sunlight. However, most natural and synthetic textile materials are at least partially permeable to UV components of sunlight. Accordingly, the mere wearing of clothing does not necessarily provide skin beneath the clothing with adequate protection against damage by UV radiation. Although clothing containing a deeply coloured dye and/or having a tight weave texture may provide a reasonable level of protection to skin beneath it, such clothing is not practical in hot sunny climates, from the standpoint of the personal comfort of the wearer. Therefore, there is also a need to provide protection against UV radiation for skin which lies underneath clothing, including lightweight summer clothing, which is undyed or dyed only in pale shades.
Commonly used UV absorbers such as benzotriazoles and benzophenone are highly effective in their UV absorber capacity. However, they are quite costly and can prove difficult to incorporate within different target media. Furthermore, UV absorbers of this type show no substantivity to hair and present handling difficulties in that they are generally produced and utilized in powder form and have relatively low melting points. A liquid, on the other hand, is much easier to handle, does not require melting, and provides more effective and thorough mixing throughout the target material.
Thus, there exists a continuing need for effective liquid UV absorbing compositions which exhibit sufficient versatility to be incorporated within or applied to different and various media and substrates.